Lean premixed combustors rely on a high degree of swirl to both promote fuel air mixing and to provide a reverse flow zone to stabilize the combustion.
Certain designs of lean premixed burners are capable of operating with a very high swirl. In such burners, a very high swirl results in very firm and robust aerodynamics which in turn promotes stable combustion and minimises issues with combustion dynamics. From a combustion perspective high swirl is therefore advantageous.
Though being good for the combustion system, a very high swirl can be damaging for the turbine, as a highly rotating vortex core can be produced in the downstream part of the combustor. On encountering the turbine, the vortex core leads to a reduction in aerodynamic performance of the turbine, and more significantly increases the heat loading on the turbine components through enhancing the heat transfer.
Present gas turbines deal with this problem by either having lower swirl for the burner, thereby reducing the robustness against flame dynamics, or increasing the robustness of the turbine to be able to deal with a highly rotating vortex core. In the case of the latter, there is additional cost due to the use of greater turbine cooling air flows, increased turbine material cost, reduced turbine life, and reduced turbine aerodynamic performance.
WO 20071096294 A1 and WO 2007/131818 A1 describe swirlers for use in a burner of a gas turbine engine, the swirlers comprising a plurality of vanes arranged in a circle, flow slots being defined between adjacent vanes in the circle, each flow slot having an inlet end and an outlet end, in use of the swirler a flow of fuel and air travelling along each flow slot from its inlet end to its outlet end such that the swirler provides a swirling mix of the fuel and air.